Received December 6, 2017; Revision received December 25, 2017
Position effect variegation (PEV) is a perturbation of genes expression
resulting from the changes in their chromatin organization due to the
abnormal juxtaposition with heterochromatin. The exact molecular
mechanisms of PEV remain enigmatic in spite of the long history of PEV
studies. Here, we developed a genetic model consisting of PEV-inducing
chromosome rearrangement and a reporter gene under control of the UAS
regulatory element. Expression of the reporter gene could be regulated
by adjustment of the GAL4 transactivator activity. Two UAS-based
systems of expression control were tested – with thermosensitive
GAL4 repressor GAL80ts and GAL4-based artificial
transactivator GeneSwitch. Both systems were able to regulate the
expression of the UAS-controlled reporter gene over a wide range, but
GAL80ts repressed the reporter gene more efficiently.
Measurements of the heterochromatin-mediated repression of the reporter
gene in the GAL4+GAL80ts system point to the existence of a
threshold level of expression, above which no PEV is observed.
KEY WORDS: heterochromatin, expression, Drosophila,
Gal4, Gal80, MiMIC, GeneSwitch